Guest columnist Robin Butler, sales and marketing director at Sherborne Sensors, investment in R&D has broadened the scope of sensor applications in military systems.
The core sensor technology powering inertial inclinometers to measure angle relative to gravity has remained relatively unchanged for several years, and has been field proven in a wide range of defence applications.
Yet the need to consistently deliver measurement precision and repeatability, under the harshest operating conditions and often in space restricted applications continues to drive the need for further customisation.
There has been renewed focus on revisiting tried and trusted sensor solutions to solve new technological challenges.
One recent example is the Helicopter Alert and Threat Termination – Acoustic (HAALT-A) project in the US, where commercial sensors were reconfigured onto a helicopter airframe to acoustically detect incoming fire and localise the shooter(s).
Since an established sensor design was used, a fully-developed and detailed deployment package was delivered within seven months of the contract award.
A servo inclinometer is an extremely sensitive transducer that converts angle of tilt into an electronic signal, and is able to determine horizontal and vertical inclination with high precision. A torque balance flexure servo inclinometer essentially consists of a pendulum and unbalanced mass that aligns itself with the Earth’s gravitational field, the deflection of the pendulum being proportional to the sine of the angle of tilt.
Typically, the pendulus mass is mounted on a flexure suspended coil that rotates within a magnetic field provided by a permanent magnet not dissimilar to that employed in a dc motor. The pendulus mass’s position is detected by an electronic proximity sensor, and the resulting error signal is used to feed current back into the moving coil restoring the pendulus mass to its original position. The restoring current is itself the analogue signal of the sine of the angle of tilt.
For applications demanding precision and repeatability several orders of magnitude greater than conventional open loop inclinometers, a closed-loop torque balance servo system is preferred, and delivers resolutions to 0.1 arc second (0.00003°).
Closed-loop, torque balanced servo inclinometers are extremely robust, and can offer high precision after withstanding severe levels of mechanical shock and vibration. Survivability via robust design is essential for sensors deployed within military platforms.
Techniques employed by sensor-based devices to enhance survivability while maintaining accuracy include fluid damping and mechanical stops. The latter is invoked within an inclinometer (or accelerometer) to prevent damage when a device is exposed to acceleration beyond its calibrated range of operation.
Meanwhile, fluid damping employs a specialised viscous fluid that encapsulates the mechanical servo mechanism in order to provide both shock protection and to act as an additional filter attenuating unwanted background vibration that ensures highly accurate output signals.
Fluid damped servo systems are available for applications demanding the most robust sensors, and offer up to 1,500g of mechanical shock protection.
In military environments, the sensor often has to operate reliably within a background of electro-magnetic interference due to the proximity of other electrical or electronic equipment. Additional filtering is therefore provided to ensure this electromagnetic compatibility.
Sensor devices are employed in defence applications where ‘situational awareness’ is critical – i.e. to provide the user with as much information as possible concerning their present circumstances in order to take the most appropriate action.
Sensors play a crucial role in enabling this situational awareness, and there has been a huge increase in the volume of information being made available to military personnel as a result.
Significant military applications for inclinometers are, fire control aiming systems and military vehicle systems.
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